Enhanced biaxial compressive strain tuning of 2D semiconductors via hot dry transfer on polymer substrates

Abstract Strain engineering is an effective tool for tailoring the properties of two-dimensional (2D) materials, of particular interest for tuning quantum phenomena. Among the limited methods available for strain engineering under cryogenic conditions, thermal mismatch with polymeric substrates provides a simple and affordable strategy to induce biaxial compressive strain upon cooling. In this work, we demonstrate the transfer of unprecedentedly large levels of uniform biaxial compressive strain to single-layer WS ₂ by employing a pre-straining approach prior to cryogenic cooling. Using a hot-dry-transfer method, single-layer WS ₂ samples were deposited onto thermally expanded polymeric substrates at 100 °C. As the substrate cools to room temperature (RT), it contracts ∼0.5%, inducing biaxial compressive strain in the WS ₂ layer. This pre-strain results in a measurable blueshift in excitonic energies compared to samples transferred at RT, which serve as not pre-strained controls. Subsequent cooling of the pre-strained samples from RT down to 5 K leads to a remarkable total blueshift of ∼200 meV in the exciton energies of single-layer WS ₂ . This energy shift surpasses previously reported values, indicating superior levels of biaxial compressive strain induced by the accumulated substrate contraction (∼1.7%). Moreover, our findings reveal a pronounced temperature dependence in strain transfer efficiency, with gauge factors approaching theoretical limits for ideal strain transfer at 5 K. This enhanced efficiency, attributed to the increase of the Young’s modulus of the polymeric substrate with decreasing temperature, is particularly relevant for strain engineering of 2D materials at low temperatures.